This invention relates to valves used in controlling the flow of fluids, and more particularly to sealing systems for sealing rotating or reciprocating elements in the valves such as valve stems.
It is desirable to prevent or to reduce to the extent possible the leakage of fluid from a valve inserted in a pipeline. This is particularly desirable in view of legislation restricting the emissions of volatile fluids into the atmosphere. With this increasing emphasis on environmental quality, leakage of gas, oil, or other toxic or hazardous fluid to the environment surrounding the valve is unacceptable. Valves having a rotating, reciprocating, sliding, or otherwise moving element, such as a valve stem, which penetrates the pressure boundary of the valve body, will subject the valve to the leakage of the fluid passing through the valve. Further, it is important to detect at the earliest possible time the leakage of the fluid around such a moving element.
Various types of valves have moving elements. One common valve is the quarter turn valve which includes a rotatable valve element that is rotated a quarter of a turn between the open and closed position for controlling fluid flow through the valve. Examples of quarter turn valves include plug valves, ball valves, and butterfly valves. Sometimes gate valves are referred to as multi-turn valves when the actuation element is a screw used to actuate the gate. A rotatable non-rising valve stem extends from the exterior of the valve into the valve body to connect with a valve member for rotating the valve member between its open and closed positions. A gate valve may also be a linear valve if the actuation of the gate is linear, i.e. a rising valve stem.
Typically, leakage through a valve is caused by the pressure differential between the pressure of the ambient environment around the valve and the pressure in the valve body cavity. Each time there is a rotation, reciprocation, or other movement of the stem within the valve body, this pressure differential tends to cause the lading, i.e. the fluids passing through the valve, to leak past the seals around the moving element. The lading may be oil, gas, chemicals or a toxic or hazardous fluid. There is potential of some minute leakage even in the stationary position of the moving element. Valves which have high cycle, i.e. the valve stems are rotated or reciprocated frequently, tend to be more susceptible to leakage around the valve stems. Although generally insignificant, molecular leakage may still occur by the lading passing through the valve by moving molecularly through the sealant by means of a type of osmosis. However, leakage by molecular migration is typically an insignificant portion of the overall leakage. Nevertheless, the reduction of any amount of leakage is important when the valve is handling a lading that is toxic or hazardous.
Valves with single seals around the moving element are eventually subject to leakage around their seals due to wear or failure of the seals between the valve body and the valve stem. In certain critical service applications, a bellows seal is provided to provide a complete hermetic seal around the valve stem. Such a system is expensive and requires a high operational cost particularly when a secondary seal containment system is required due to the regular failure rates of bellows type seals. This is particularly true of quarter turn valves and high cycle valves.
U.S. Pat. No. 5,129,625 discloses a live load packing system for sealing an operating valve member in a fluid valve. A lantern ring is placed around the valve stem and between two packing sets. The lantern ring communicates with the valve exterior to permit lubricating fluid to be inserted into the packing bore. A series of Bellville disk springs are disposed around the valve stem and bear on a guide sleeve for compressing the packing sets. Bolts are threaded into the valve bonnet to tighten a packing flange which causes the Bellville disk springs to be compressed and in turn compress the packing sets.
U.S. Pat. No. 5,170,657 discloses an apparatus and method for detecting fluid leakage into a space sealed by a fluid seal exposed to a pressurized fluid from a flow line or pressure vessel. The leaked fluid is communicated to a piston chamber in a fluid indicator device. Upon reaching a predetermined fluid pressure, the piston is actuated for extending an indicator rod for visual observation.
U.S. Pat. No. 4,972,867 discloses a valve stem leak detection apparatus which includes a leak detection tube 172 that extends through the valve jacket and communicates with a seal chamber. In the event of leakage past the primary seal, leakage is detected by a conventional fluid detector, such as a gas detector, which is connected to the seal chamber.
U.S. Pat. No. 4,197,531 discloses an alarm system for excessive leakage across the engaging faces of a mechanical seal on a rotating shaft. A barrier fluid from a reservoir is supplied by a filler pump to a seal cavity between double mechanical seals. The pump runs for a length of time necessary to bring the pressure of the liquid in the seal cavity to that of the shut off setting of a pressure switch on the pump. If leakage is excessive, the pump must operate with abnormal frequency and an alarm system is provided to sense this abnormal pump operation.
A need exists for a retrofittable seal structure which may be added to the valve to contain and sense leakage around the seal structure of the valve and prevent leakage of the lading to the environment surrounding the valve.
The present invention overcomes the deficiencies of the prior art.